Asthma Following the 2001 World Trade Center Attack—Reply

In Reply: The limitations in our study that Dr Miller notes are common to any study in which participation is voluntary and health conditions are self-reported. The most serious are selective self-reporting among exposed persons and oversurveillance by local physicians; both limitations were discussed in the article and in previous studies from our group.^1- 4 While these potential biases undoubtedly exist, we believe they do not fully explain our main conclusions. We observed strong associations between asthma and intense dust cloud exposure in all groups, regardless of how they were recruited into the registry, whether by prior identification through lists or by self-identification. Significant exposure-response relationships were observed for exposure metrics unique to each group (length of time worked, amount of dust in the home or office), including among nonoccupationally exposed groups not being closely followed in other World Trade Center special studies. Furthermore, we had previously reported that respiratory protection was associated with a lower risk of asthma among workers on the pile.¹